Light-sensitive polymeric compounds

ABSTRACT

Light sensitive cyanuric azide polycondensates which are capable of becoming insoluble in selected solvents upon exposure to light and which are useful in the preparation of photo-mechanical resist compositions.

The present invention relates to light sensitive polymeric compounds,their preparation, and to light-sensitive compositions containing thesame.

In particular, this invention relates to light-sensitive cyanuric azidepolycondensates.

In the ensuing description, reference is made to the accompanyingdrawings, wherein are set out certain structural chemical formulae,serially numbered for identification and further described below.

It is known that polymeric compounds have been used in photo-mechanicalprinting processes as light-sensitive agents. Thus, light-sensitivepolymeric compounds have been used to produce positive or negativephotographic relief images on the surface of substrates by coating thesurface of a substrate with light-sensitive composition containing thecompounds, exposing at least one part of the coating to irradiatedlight, removing either the exposed or the unexposed part of the resistcoating and treating the surface of the substrate (for example, byetching or electroplating) to produce an appropriate positive ornegative replica of the exposed area on the surface of the substrate.

However, prior to the present invention the production ofphoto-mechanical resist compositions on the surface of substrates hadcertain disadvantages, such as a low resolution, poor edge definition ofthe projected image, pin-hole and other defects in the developed image,such as poor adhesion of the resist coating to the substrate and undueoxidation or instability of the resist coating.

From British Patent Specification Nos. 843,541 and 843,542 it is knownthat film-forming, light-sensitive synthetic polymers which are capableof becoming insolubilised on exposure to light may be prepared wherebythe polymers contain a substantial proportion of side-chains which have--N₃ groups attached to carbon aroms therein with not more than two --N₃groups attached to any one side-chain. Such light-sensitive polymers aredescribed and represented as ##EQU1## in which formula U represents therecurring atoms of the polymer chain proper and Z is a linkage joiningthe azide group. Typical linkages described are given as bivalentradicals of aromatic substances.

The azide group, however, is very reactive and it is particularlydifficult to polymerise aromatic azido groups to producelight-sensitive, stable polymeric compounds.

We have discovered that it is possible to prepare stable, novel,light-sensitive polymeric compounds which are suitable for use eitheralone or in the form of their compositions in photo-mechanical processesby being insolubilised to selected solvents on exposure to light.

According to the present invention there are provided light-sensitivepolymeric compounds as represented by the general formula I ##EQU2## INWHICH FORMULA N IS A WHOLE NUMBER FROM 2 TO 120 AND

R represents a

Phenylene - 1,3,

Phenylene - 1,4,

1-phenylcarbonyl-phenylene - 2,4,

1-phenylcarbonyl-phenylene - 2,6,

2,2'-diphenylcarbonyl or

2,3'-diphenylcarbonyl group

or an

1-alkylcarbonyl-phenylene - 2,5,

1 - alkylcarbonyl-phenylene - 2,4 or

1 - alkylcarbonyl-phenylene - 2,6 group

in which the alkyl group contains from 1 to 4 carbon atoms, a

naphthylene - 2,7

naphthylene - 2,6 or

naphthylene - 2,4 - group

wherein the phenyl groups, if desired, are substituted with one or twoalkyl groups containing from 1 to 4 carbon atoms or a phenyl group.

The azido group, represented as -N₃, formula I above, may alternativelybe represented as the resonant structure

    --N.sup.(.sup.-) --N.sup.(.sup.+) .tbd.N⃡--N=N.sup.(.sup.+) =N.sup.(.sup.-)

wherein the photosensitivity of the polycondensate is believed to becaused by decomposition of the azido group by energy received fromirradiated actinic light to give rise to free valencies which form bondsby further crosslinking with neighbouring polycondensate moleculethereby increasing the insolubility of polycondensate in the exposedregion.

In one preferred embodiment, light-sensitive compounds according to theinvention are wherein R represents a naphthylene 2,7 group, a1-benzoyl - phenylene - 2,4 group, a 1-benzoyl - phenylene - 2,6 group,a 1-acetylphenylene - 2,4 or a phenylene - 1,3 group.

In another embodiment, light-sensitive polymeric compounds according tothe invention are wherein R represents an 1-alkylcarbonyl-phenylene -2,6, for example wherein the alkyl group is a methyl group, a1-alkylcarbonylphenylene 2,5, a 2,3'-diphenyl carbonyl, a 2,2'-diphenylcarbonyl, a phenylene - 1,4 or a naphthylene - 2,6 group.

According to another aspect of the invention there are providedlight-sensitive compositions comprising a polymeric compound accordingto the invention mixed with, dissolved or dispersed in an inert carrier.

The polymeric compounds or light-sensitive compositions preparedtherefrom may also be mixed with or contain additives and/orlight-sensitive agents.

Preferably, the polymeric compounds are dissolved in a suitable organicsolvent with, if desired, an inert diluent. Particularly suitablelight-sensitive polymeric compositions are solutions which contain1,4-dioxane, toluene or cyclohexanone.

Preferably the polycondensation may be exposed to actinic light from anysource and of any type. Suitable sources include irradiation frommercury vapour lamps, argon globe lamps, tungsten lamps, carbon arcs andphotographic flood-lamps, although a strong light source is notnecessarily required to initiate decomposition of the azido group andthe subsequent cross-linkage with neighbouring polycondensate molecules.This is especially true for compositions when optical sensitizers, interalia, are incorporated into the composition. Thus, the light-sensitivityand photo-condensation property of compounds as represented by formula Imay be increased; for example by incorporating an optical orlight-sensitizer into a composition which contains polycondensatesaccording to the invention, such as Michler's ketone(4,4'-tetramethyldiaminobenzophenone). Other suitable optical orlight-sensitizers which may be incorporated into compositions accordingto the invention are p,p'-tetraethyldiamino-diphenylketone;p,p'-tetramethyldiaminodiphenylketone; p,p'-dimethylaminobenzophenone;1,2-benzanthraquinone, β-chloroanthraquinone; 9,10-anthraquinone;4-nitro-chloro aniline; 2,6-dichloro4-nitro-aniline;2,4,6-trinitroaniline; 5-nitro-2-aminotoluene; and p-nitrodiphenyl.

The light-sensitizers may be incorporated into the polycondensatetogether with other solid or liquid carrier materials if required,during manufacture of the polymeric compounds according to theinvention, or subsequent to their preparation, for example, on theapplication of the compound or the composition containing the compoundto a substrate.

The invention also provides light-sensitive coatings when coated on asubstrate with a compound or a composition according to the invention.

In a further aspect the invention provides a method of preparinglight-sensitive polymeric compounds of formula 1 comprising condensing,in the presence of a common solvent, a cyanuric azide dihalide asrepresented by formula II ##EQU3## in which formula X represents ahalogen atom with an alkali metal salt of a dihydroxy aromatic compoundas represented by formula III ##SPC1## in which formula

R₁ represents a hydrogen atom or a hydroxy group,

R₂ represents a hydrogen atom, a hydroxy group, an alkyl groupcontaining from 1 to 4 carbon atoms or a phenyl group,

R₃ represents a hydrogen atom, a hdyroxy group, an alkyl groupcontaining from 1 to 4 carbon atoms or a phenyl group, and

R₄ represents a hydrogen atom, an alkyl group containing from 1 to 4carbon atoms, a phenyl group, a R₅ CO- group in which R₅ is an alkylgroup containing from 1 to 4 carbon atoms, a phenyl group or a hydroxyphenyl group,

with the proviso that only one of R₁, R₂ and R₃ does represent a hydroxygroup, and R₂ and R₃ may together form a tetramethylene group ortogether with the carbonatoms to which they are bound a benzogroup thatis substituted with a hydroxy group.

Suitable dihydroxy aromatic starting materials for preparing compoundsaccording to the invention are 1,3-dihydroxybenzene,1,4-dihydroxybenzene, 2,4-dihydroxy acetophenone, 2,5-dihydroxyacetophenone, 2,6-dihydroxy acetophenone, 2,4-dihydroxy propiophenone,2,5-dihydroxy propiophenone, 2,6-dihydroxy propiophenone, 2,4-dihydroxybutyrophenone, 2,5-dihydroxy butyrophenone, 2,6-dihydroxy butyrophenone,2,4 dihydroxy valerophenone, 2,5-dihydroxy valerophenone, 2,6-dihydroxyvalerophenone, 2,4-dihydroxy benzophenone, 2,5-dihydroxybenzophenone,2,6-dihyroxybenzophenone, 2,2'-dihydroxybenzophenone,2,3'-dihydroxybenzophenone, and 2,4'-dihydroxy benzophenone.

Preferably cyanuric azide dichloride is condensed with the sodium saltof 2,7-dihydroxy naphthalene, 2,4-dihydroxy benzophenone, 2,6-dihydroxybenzophenone, 2,4-dihydroxy acetophenone or 1,3-dihydroxybenzene.

In the method 1 mole of cyanuric azide dichloride may be condensed with1 mole of the sodium salt.

The condensation reaction between the alkali metal salt of a dihydricaromatic compound and cyanuric azide dihalides may be carried out in anyconvenient solvent, providing at least one of the starting materials andthe polycondensate so formed are soluble in the solvent selected. In oneembodiment, the dialkali metal salt of 2,7-dihydroxy naphthalene iscondensed with cyanuric azide dihalide dissolved in a water-miscibleorganic solvent. A suitable water-miscible solvent may be selected fromthe group consisting of aldehydes, ketones and alcohols, particularlywhen the alkyl group contained therein has from 1 to 3 carbon atoms.

Preferably, one mole equivalent of a dialkali metal salt of thedihydroxy aromatic compound is condensed with one mole equivalent of thedihalo cyanuric azide. Polycondensates according to the invention have awide range of light-sensitivity, good film-forming properties,transparency and flexibility and possess good adhesive characteristics.The polycondensates prior to exposure to actinic light are particularlysoluble in solvents such as toluene, xylene, and cyclohexanone, andafter exposure to actinic light are insoluble in these solvents.Furthermore, the insolubilized polymer is resistant to acids and alkalisused in etching and electroplating processes.

The present invention also provides a process suitable for use inphotomechanical reproduction printing processes, comprising exposing alight-sensitive polycondensate according to formula I as described aboveto actinic light through a photographic mask, said polycondensate beingin the form of a self-supporting film of the compound according toformula I or as a coating on a substrate, said exposure continuing untilthe azido group of the polycondensate in the exposed regions isdecomposed, followed by selectively removing the polycondensate from theunexposed regions by treating with a solvent. The polycondensate ispreferably applied to the surface of the substrate in the form of asolution by being dissolved in an organic solvent such as toluene,xylene or cyclohexanone, and after exposure to light the polycondensatein the non-exposed regions is preferably removed by the same solvent.

The polycondensates according to the invention may have a heterogeneouscomposition in that the may be formed of structural units of differentmolecular weight compounds, the particular type and molecular weightrange of the recurring structural unit being determined by the choice ofthe starting materials and the amount of cross-linkage after exposure tolight.

The cyanuric azide dihalide selected is preferably cyanuric azidedichloride, as represented by formula II, which may be prepared inaccordance with the method described by C. V. Hart, J. Am. Chem. Soc.,50, 1922 (1928).

Substrates suitable for the coating with polycondensates according tothe invention may be selected from natural or synthetic solid materialsand/or composites of the same, providing the surface is suitable tosupport the polycondensate. Particularly suitable substrates are laminarmaterials such as metal sheets, for example copper, aluminium, magnesiumand zinc sheets or plates, composite laminated sheet materials, forexample copper-clad/phenol formaldehyde laminates, and plastics foilmaterials such as polyvinyl acetal, cellulose esters, polyethyleneterephthalate and polystyrene foils. Other suitable substrates aresemiconductor materials, such as silicon, germanium, or germaniumsilicon alloys and metallic oxide semiconductors such as copper oxide.Solutions of the polycondensates according to the invention may becoated onto the surface of a substrate and allowed to dry.

The desired thickness of a coating on the substrate is chosen inaccordance with the type and molecular weight of the recurringstructural unit(s) in the polycondensate and also in accordance with theintensity of the irradiated light, the exposure time and the degree ofcross-linkage for the insolubilised regions of the polymeric coating.

By way of illustration, certain preferred processes embodying theinvention will now be described in more detail in the ensuing specificExamples:

EXAMPLE 1

Cyanuric chloride, 36.8 grams (1/5 mol), was dissolved in 200 ml acetoneagitated in a 400 ml beaker. Sodium azide, 13 grams (1/5 mol), dissolvedin 100 ml of water, was added to the cyanuric chloride solution dropwiseover approximately 10 minutes and the solution agitated for a further 15minutes, then poured into an evaporating dish and left standingovernight. The following day the crystals of cyanuric azide dichloridewere separated by filtration, washed with 100 ml of water, then placedin a silica gel filled desiccator to dry. Yield 32.4 grams; m.pt. 85°C.

1.6 grams of 2,7-dihydroxy naphthalene (1/100 mol) and 0.8 grams ofsodium hydroxide were dissolved in 100 ml of water in a 250 ml beaker toform the sodium salt. Cyanuric azide dichloride, 1.91 grams (1/100 mol),was then dissolved in 50 ml acetone. The sodium salt solution wasagitated and the cyanuric azide dichloride solution was added to thestirred solution. A white polymeric precipitate formed, and thesuspension was heated to 60°C and kept at this temperature for 30minutes with agitation. After cooling to room temperature, theprecipitate was filtered and washed with water. It was then dried in anair-circulating oven at 70°C. Yield of white polymer 2.67 grams.

EXAMPLE 2

The procedure according to Example 1 was repeated except that 2.14 gramsof 2,4-dihydroxy benzophenone were used instead of the 2,7-dihydroxynaphthalene.

EXAMPLE 3

The procedure according to Example 1 was repeated except that 2.14 gramsof 2,2'-dihydroxy benzophenone were used.

EXAMPLE 4

The procedure according to Example 1 was repeated except that 1.52 gramsof 2,4-dihydroxy acetophenone were used.

EXAMPLE 5

The procedure according to Example 1 was repeated except that 1.1 gramsof 1,3-dihydroxybenzene were used.

EXAMPLE 6

The polymers obtained by the process described in Examples 1 to 5 wereeach dissolved in cyclohexanone and the solutions were used to dipcoat aseries of copper clad laminates with the resist coatings and thecoatings were dried in air by evaporation of the solvent at 65°C.Exposure of the resist coatings through a mask to U.V. light for 5minutes, and development in toluene to remove the unexposed regions,yielded an image in each case of resist coating on the laminate whichallowed the copper of the non-coated regions to be etched in a ferricchloride solution.

EXAMPLE 7

The polymer solutions obtained according to Example 6 were taken and 10%by weight of Michler's ketone were dissolved in them. The solutions wereapplied to a silicon oxide surface of silicon slices by a spincoatingtechnique at 6000 r.p.m. The coated slices were stoved for 5 minutes at70°C, then exposed in a vacuum chamber through a photomask to short-waveU.V. light (intensity 4.7 milliwatts per sq.cm.) for from 21/2 to 30seconds. The photoresist coatings were then developed by 1 minute'simmersion in toluene. The silicon oxide films were then etched inhydrofluoric acid. A resolution of 0.5 micron windows was obtained.

What we claim is:
 1. A light-sensitive polymeric compound of the formulaI ##EQU4## in which formula n is a whole number from 2 to 120 andRrepresentsphenylene - 1,3 phenylene - 1,4 1- phenylcarbonyl-phenylene -2,4 1- phenylcarbonyl-phenylene - 2,6 2,2' - diphenylcarbonyl 2,3' -diphenylcarbonyl or an1 - alkylcarbonyl-phenylene - 2,5 1 -alkylcarbonyl-phenylene - 2,4 1 - alkylcarbonyl-phenylene - 2,6in whichthe alkyl group contains from 1 to 4 carbon atoms, a naphthylene - 2,7naphthylene - 2,6 or naphthylene - 2,4 - groupwherein the phenyl groups,if desired, are substituted with one or two alkyl groups containing from1 to 4 carbon atoms or a phenyl group.
 2. A light-sensitive compoundaccording to claim 1 in which R represents a 2,2' - diphenyl carbonylgroup.
 3. A light-sensitive compound according to claim 1 in which Rrepresents a naphthylene - 2,7 group.
 4. A light-sensitive compoundaccording to claim 1 in which R represents a 1-benzoyl phenylene - 2,4group.
 5. A light-sensitive compound according to claim 1 in which Rrepresents a 1-acetyl phenylene - 2,4 group.
 6. A light-sensitivecompound according to claim 1 in which R represents a phenylene - 1,3.